Oberthürite

Chemical formula: Rh₃Ni₃₂S₃₂

Oberthürite is an extremely rare rhodium-nickel sulfide, forming microscopic, metallic inclusions in other minerals.

## Characteristics Oberthürite is a rhodium-nickel sulfide, occurring as extremely small, rounded or irregular grains, usually not exceeding 100 micrometers in size. It is observed as inclusions in chromite crystals and other sulfides. Due to its microscopic size, its visual characteristics are difficult to assess without specialized equipment. In reflected light, it has a creamy-white color with a pinkish hue. ## Physical Properties As an opaque mineral, oberthürite is characterized by a metallic luster. Its hardness and density have not been precisely measured due to the size and mode of occurrence of the grains, however, the density calculated based on the chemical formula and unit cell parameters is 6.55 g/cm³. ## History and Name The mineral was officially recognized by the International Mineralogical Association (IMA) in 2017 (IMA2017-081). The name honors Thomas Oberthür, a German geologist and mineralogist, for his significant contributions to research on the mineralogy of platinum-group metals, especially concerning the Great Dyke deposit in Zimbabwe, from where the holotype originates. ## Uses Oberthürite has no industrial or commercial applications. Its significance is purely scientific and collector-oriented, as an extremely rare representative of platinum-group metal mineralization.

Properties

Luster: Metallic
Density: 6.55
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Cubic

Diagnostic features

## Identification Identification of oberthürite is possible only through advanced laboratory techniques, such as reflected light ore microscopy and chemical analysis using an electron microprobe (EDS/WDS). In reflected light, it exhibits a creamy-white color with a pinkish hue and is isotropic. ## Distinguishing from Similar Minerals It can be confused with other nickel and platinum-group metal sulfides, such as pentlandite, kuvaevite, horomanite, or mironovite. Definitive differentiation requires chemical composition analysis, as all these minerals form similar microscopic, metallic grains. ## Crystal Forms Oberthürite occurs as anhedral (irregular), rounded grains and aggregates, typically ranging from 10 to 100 micrometers in size. No well-formed crystal faces have been observed.

Geological environment

## Genesis Oberthürite forms in ultramafic layered intrusions. It crystallizes in the late stages of magmatic processes from a sulfide liquid rich in nickel, copper, and platinum-group metals. In the type locality (Unki mine), it is associated with a sulfide horizon within the Great Dyke magmatic complex. ## Mineral Associations This mineral co-occurs with chromite (as inclusions), pentlandite, chalcopyrite, pyrite, kuvaevite, braggite, cooperite, and other, as yet unnamed, platinum-group metal sulfides and alloys. ## Localities The only confirmed occurrence of oberthürite worldwide is the Unki platinum mine, located in Shurugwi, within the Great Dyke magmatic intrusion in Zimbabwe.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of an oberthürite specimen is defined solely by the confirmation of its presence through scientific analysis. Since the mineral is microscopic, its visual characteristics, such as color or form, are not relevant for collector assessment. The most valuable samples are those with the highest number of identified oberthürite grains, rich in associated minerals, and originating from the type locality.

Care and storage

## Cleaning Specimens in which oberthürite has been identified should be cleaned with the utmost care, preferably using compressed air to remove dust. Any form of mechanical or chemical cleaning is highly inadvisable, as it can irreversibly damage the microscopic mineral grains. ## What to Avoid Avoid contact with chemicals, acids, and ultrasonic cleaners. Temperature and humidity changes do not directly affect the mineral itself, but they can harm the host rock matrix. ## Storage Specimens containing oberthürite, due to their scientific value and rarity, should be stored in stable conditions, in sealed "micromount" boxes, protecting them from dust and mechanical damage. It is best to keep them in a dry place, away from direct sunlight.

Sources

IMA Mineral List (CNMNC)